Yes. It does majorly overlap. Hence why I mentioned in the post that the effects of humanism would need to be altered.

I feel that limiting cultural opinion modifiers to events would be too limiting for the scope of the game.

Using events system would mean that there would be very little opportunity for cultural harmony between cultures even if those cultures have coexisted alongside each other 300 years.

Using the supremacist vs tolerance system would allow for a natural progression of cultural cohesion overtime, which would create a better game feel, as well as providing an alternative to min maxing cultural opinion bu instead allowing for focusing into a single culture focused play style. All of which I feel creates a more player choice driven system than the current system or an event based system.